Cardiac mapping catheter

ABSTRACT

A multi electrode catheter for non contact mapping of the heart having independent articulation and deployment features.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application and claims priority under35 U.S.C. §120 to U.S. patent application Ser. No. 13/289,367, filed onNov. 4, 2011, which is a continuation of U.S. patent application Ser.No. 12/005,975, filed on Dec. 28, 2007, now U.S. Pat. No. 8,103,327, theentire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to a catheter for use inside thehuman heart during medical procedures. The catheter can be used for“non-contact” mapping of the electrical activity of the heart, forlocating and reporting the position of other procedure catheters withinthe heart, and for other purposes. The catheter includes an electrodearray that can be deployed and retracted independently from catheterarticulation.

BACKGROUND OF THE INVENTION

Cardiac arrhythmias are a leading cause of stroke, heart disease, andsudden death. The physiological mechanism of arrhythmia involves anabnormality in the electrical conduction of the heart. There are anumber of treatment options for patients with arrhythmia that includemedication, implantable devices, and catheter ablation of cardiactissue.

Traditionally, the arrhythmia is studied and diagnosed by “electricallymapping” the heart with catheters inserted through the vasculature intoa heart chamber. Traditionally, the electrical activity of the heart isacquired directly by “in-contact mapping” of the interior wall surfaceof a heart chamber. In this technique electrodes are placed in intimatecontact with the heart wall and the voltage at that location is recordedand plotted against time for display to the physician. The in-contactcatheters may be large and essentially fill the entire heart chamber, orthey may be smaller and moved around in the heart chamber tosequentially map various areas of the heart. Mechanically, thein-contact mapping catheters are “soft” so that they can conform to theheart chamber. Softness is required so the electrodes come into intimatecontact with the heart wall while accommodating wall motion of thebeating heart.

For example, multiple electrode in-contact mapping catheters are knownfrom U.S. Pat. No. 5,628,313 to Webster that shows a so-called “basket”catheter. In use, this very flexible and conformal catheter is deployedin the heart and presses individual electrodes against the chamber wallfor full chamber contact mapping of a beating heart. Smaller multipleelectrode catheters are known as well. For example, the U.S. Pat. No.5,279,299 to Imran illustrates techniques for creating smaller catheterarrays that are used to selectively contact map portions of the cardiacchamber. This catheter is flexible and electrodes remain in contact withthe wall even when the catheter shaft is displaced slightly. In each ofthese examples, the limbs of the catheter are very flexible and gentlycontact the chamber wall while the wall of the heart is moving.

“Non-contact mapping,” also known in the art, is an alternative toin-contact mapping where a catheter array positioned within a chamber isused to collect global electrical information. This global informationis then used to compute a solution to the so-called “inverse problem”.The inverse problem of electrophysiology is the calculation of wallelectrical potentials from the measured field voltages associated withthe wall potentials as measured within the blood pool remote from thechamber wall. The mathematical “solution” displayed to the physician isthe computed wall surface voltages that can be used to detect problemsin electrical conduction in the heart wall.

Although in-contact and non-contact catheters are used for the samepatient indications, they have very different mechanical and electricalrequirements. Chief among the requirements of a non-contact catheter isstability of the electrode array. The geometry and locations of theelectrodes are assumed for the inverse solution calculation and need tobe known with great precision. Small error in electrode position canrender large discrepancies in computed mathematical solution. Inaddition, controlled movement of the electrode array within the chamberof interest is necessary in order to improve the accuracy of thenon-contact map. Deployment of the electrode array into a repeatableprecisely known shape, while supporting controlled movement of thecatheter, pose particularly complex and novel requirement on thecatheter design.

Once the anatomic origin of problems in electrical conduction areidentified, the physician may proceed to ablate the offending tissue,thus treating the arrhythmia. Catheter ablation procedures have evolvedin recent years to become an established treatment for patients with avariety of supraventricular and ventricular arrhythmias. The typicalcatheter ablation procedure involves mapping of the heart tissue inorder to identify the site of origin of the arrhythmia, followed by atargeted ablation of the site with an RF catheter. The procedure takesplace in an electrophysiology laboratory and takes several hours most ofwhich is spent mapping the electrical conduction in the heart.

Although in-contact and non-contact mapping methods are known in the artand various deflectable, displaceable and deployable catheters are knownas well, there is a continuing need to improve the accuracy, stabilityand maneuverability of such devices so that they can be more widelyused, especially as an adjunct to cardiac ablation procedures.

SUMMARY OF THE INVENTION

The present invention is an intravascular catheter that may be deployedwithin a heart chamber placing multiple electrodes in a known spatialconfiguration. The catheter may be used to map electro-anatomicalcharacteristics of the heart and/or to locate and position othercatheters within the heart. Adoption of the inventive construction ofthe present catheter provides a device that is smaller, less expensiveto manufacture, maneuverable, and stable in its deployed configuration.Electrode stability makes the device much more accurate and therefore,of more value to the physician. The design and construction also makethe device smaller in cross section than existing designs and therefore,more easily used by a physician and better tolerated by the patient. Asset forth in detail hereafter, the distal array of the catheter isfabricated as a flexible printed circuit. The deployment andarticulation functions of the catheter are very independent of eachother.

Two separate embodiments of the deployment mechanisms are disclosed. Incontrast to prior art devices both of these mechanisms permit thedeployment function to operate wholly independently from thearticulation or deflection feature of the catheter. The independence ofthe deployment feature and the articulation feature together withinnovative structural features and materials create a noncontact mappingcatheter that is easily placed and used with a very stable electrodegeometry.

BRIEF DESCRIPTION OF THE DRAWINGS

An illustrative embodiment of the invention is shown in the severalviews of the figures. The use of identical reference numerals throughoutthe several figures and views indicate the same element of the device,wherein;

FIG. 1 is a schematic diagram showing the catheter in the context of thesystem;

FIG. 2A is a schematic diagram showing the catheter;

FIG. 2B is a schematic diagram showing the catheter;

FIG. 2C is a schematic diagram showing the catheter;

FIG. 3A is a schematic diagram showing the distal portion of thecatheter;

FIG. 3B is a schematic diagram showing the distal portion of thecatheter;

FIG. 4A shows a step in the construction of the distal portion;

FIG. 4B shows a step in the construction of the distal portion;

FIG. 4C shows a step in the construction of the distal portion;

FIG. 4D shows a step in the construction of the distal portion;

FIG. 5A shows a step in the manufacture of the distal portion;

FIG. 5B shows a step in the manufacture of the distal portion;

FIG. 6A shows the flexible printed circuit in plan view;

FIG. 6B shows the flexible printed circuit in cross-section;

FIG. 7 shows a metallization layer of the flexible printed circuit;

FIG. 7A shows a portion of the metallization layer of the flexibleprinted circuit of FIG. 7;

FIG. 7B shows a portion of the metallization layer of the flexibleprinted circuit of FIG. 7;

FIG. 7C shows a portion of the metallization layer of the flexibleprinted circuit of FIG. 7;

FIG. 8A shows the spline assembly formed from a flexible printed circuitin plan view;

FIG. 8B shows the spline assembly formed from a flexible printed circuitin cross-section view;

FIG. 8C shows a distal array segment in projection view;

FIG. 8D shows a spline in cross section;

FIG. 8E depicts a portion of a spline of FIG. 8D;

FIG. 9A shows the spline assembly formed from a flexible printed circuitin plan view;

FIG. 9B shows the spline assembly formed from a flexible printed circuitin cross-section view;

FIG. 9C shows a distal array segment in projection view;

FIG. 9D shows a spline in cross section;

FIG. 9E depicts a portion of the spline shown in FIG. 9D;

FIG. 10A shows a first embodiment of the deployment actuator;

FIG. 10B shows a first embodiment of the deployment actuator;

FIG. 11 shows a distal array segment in projection view;

FIG. 12 shows a distal array segment in projection view;

FIG. 13 shows a distal array segment in projection view

FIG. 14 shows a partial section of a distal segment with an additionalfeature;

FIG. 15 shows simplified schematic of second embodiment of thedeployment actuator showing complimentary distal and proximal springs;

FIG. 15A shows a portion of the actuator of FIG. 15;

FIG. 16A is a simplified schematic of the catheter;

FIG. 16B is a simplified schematic of the catheter;

FIG. 16C is a simplified schematic of the catheter; and,

FIG. 17 is a plot of force against displacement of several structures inthe catheter.

DESCRIPTION OF THE INVENTION

FIG. 1 depicts the context of the invention. The figure shows a highlyschematic view of the overall system that includes the physician,patient, catheters, and related electrophysiology equipment locatedwithin an operating room. The physician 16 introduces the catheter 10into the vasculature of the patient 11 at the patient's leg and advancesit along a blood vessel ultimately, entering the patient's heart 12.Other catheters that may be used in the procedure are represented bycompanion catheter 18. Each catheter is coupled to signal conditioninghardware 20 with appropriate catheter cabling typified by catheter cable17. The signal, conditioning hardware 20 performs various interfacefunctions applicable to the mapping, tracking, and registrationprocedures that are performed in conjunction with the workstation classcomputer-processing unit 24. If the companion catheter 18 is an ablationcatheter, then conditioning hardware also forms an interface to an RFablation unit (not illustrated). Three patent applications all publishedDec. 27, 2007 are incorporated by reference herein to further explainthe use of the catheter for non-contact mapping as follows: 20070299353;20070299352 and 20070299351.

In use, the physician looks at a computer display 26. Present on thedisplay is a substantial amount of information. A large window presentsan image of the heart chamber 13 along with an image of the catheter 10.The physician will manipulate and control the catheter 10 based in parton the images and other data presented on the display 26. The image 27seen in FIG. 1 is schematic and depicts the distal array of the catheter10 deployed, occupying a small portion of the heart chamber 13 volume.The representation of the heart chamber 13 may use color, wire frame, orother techniques to depict the structure of the heart chamber 13 and tosimultaneously portray electrical activity of the patient's heart. It isregarded as useful to display chamber geometry, catheter location, andelectrical activity in an integrated fashion on the display 26. In use,the physician will observe the display 26 and interact with theworkstation processing unit 24 and the catheters 10 and 18, to directthe therapy as a medical procedure.

FIG. 2 A through FIG. 2 C depicts array deployment and catheterarticulation along with the associated positions of the handle controls.FIG. 2A shows the catheter in isolation. The catheter 10 has an elongatebody 31 with a distal end 37 and a proximal end 39. The elongate body 31includes a tubular sheath 35. The proximal end 39 connects to anassembly that includes a handle segment 30. The physician may manipulatethe handle segment 30 to selectively deflect, deploy, and rotate thecatheter to perform the medical procedure. The handle segment 30 iscoupled to an elongate intermediate section or segment 32. Theintermediate section is coupled to a deflection segment 34, which inturn is coupled to a distal array segment 36, located at the distal tipor end 37. Not shown is the catheter cable 17 used to connect theelectrodes on the distal array segment 36 to the signal conditioninghardware 20. In FIG. 2A the catheter 10 is in the undeflected andundeployed state where the distal array segment 36 is collapsed and thedeflection segment 34 is straight. In this configuration, the catheteris introduced into the body using the familiar Seldinger technique.

FIG. 2B shows the catheter 10 with the handle segment 30 manipulated todeploy the distal array segment 36 into the open or deployed state. Inone embodiment, the pommel 33 of the handle assembly 30 is movedretrograde with respect to the handle assembly as indicated by motionarrow 38 to deploy the distal electrode array segment 36. In thisembodiment, the pommel 33 will lock into position to deploy the array36. To set the lock, the pommel 33 will have to be pulled enough toovercome a modest spring force to reach a detent position. Whendeployed, the distal array segment 36 opens to place electrodes into theoperating position. In alternative embodiments the deployment controlmay be turned or rotated to deploy the electrode array.

FIG. 2C shows activation of the deflection segment 34. Antegrade motionof the handle ferrule 42 of the handle segment 30 depicted by motionarrow 40 deflects or articulates the deflection segment 34. Note thatthe catheter 10 responds to this motion and the deflection segment 34forms an are confined to a single plane. In the figure, the articulationor deflection motion lies in the plane of the page. The deflectionoperation causes the distal array segment 36 to be pointed up to 180°from the initial direction shown in panel 2A. The phantom dottedposition seen in the figure shows that this articulation may besymmetrically “bi-directional.” It should also be understood that thearticulation may also be asymmetrically bi-directional such that the arcshape is different in each direction. In one embodiment, best depictedin Fig. IS, articulation or deflection of the segment 34 moves a pullwire from the center axis of the catheter and it moves off to the sidewithin the catheter body. This displacement of the pull wire reducestension in the pull wire and leads to the deflection.

Thus it is shown that the catheter 10 has an elongate body 31 having adistal end 37, and a proximal end 39, and an elongate central axis. Aproximal handle segment 30 having an articulation control 42 and adeployment control 33 are attached to the proximal end 39. There is anintermediate segment 32 connected to the handle and a deflectablesegment 34 connected to the intermediate segment 32. The deflectablesegment 34 will articulate in a plane through an angle in response tothe articulation control. Also a distal array segment 36 is connected tothe deflectable segment 34. This distal array segment 36 includes adeployable distal electrode array that can move from a first retractedposition depicted in FIG. 2A to a second deployed position depicted inFIG. 2B. The deployment mechanism coupled to said deployment controlcouples the motion of the deployment control to operate the distalelectrode array segment which causes the distal array segment to deployinto said second deployed position, independently of the operation ofsaid articulation control.

The physician can rotate the handle segment 30 and operate ferrule 42 toposition and “aim” the distal array segment 36 toward any part of thecardiac anatomy within the heart chamber. When deployed, the varioussplines typified by spline 50 carry various electrodes into specifichighly stable and reproducible spatial locations.

FIG. 3A and FIG. 313 depict the distal array segment 36 in the deployedand undeployed states and serve to illustrate the location of theelectrodes. FIG. 3A shows the distal array segment 36 in isolation andin the retracted or undeployed 43 state or condition. The drawing showsa uniform and symmetrical distribution of the electrode sites astypified by electrode 54 along the length of a typical spline 50. It maybe useful to place more of the sensing electrodes near the most distalend or tip 37 of the distal array segment 36. An asymmetrical electrodedistribution may be advantageous for non-contact mapping functions. Inaddition to multiple sensing electrodes, current injecting locatorelectrodes, typified by locator electrode 55, may be placed at alocation along the spline 50. In general it is preferred to positionlocator electrodes so that they are far apart in the deployed sate.Current sourcing or sinking for the locator electrodes may also takeplace from ring electrodes 57 and tip electrode 53. Tip electrode 53 mayalso be provided for cardiac stimulation, ablation or as a locatorelectrode.

In summary, the splines 50 of the distal electrode array segment 36 maycarry various sets of independent electrodes 54. Typically sixty-foursensing electrodes will be distributed over and along the varioussplines 50. Several locator electrodes may be positioned diametricallyopposed to each other as illustrated by example, on the meridian of thedeployed shape. Optionally other electrodes may occupy space in thedistal electrode array. In use, sets of the electrodes are used atvarious times or concurrently during the medical procedure.

FIG. 3B shows the distal array segment 36 in the deployed state 41.Together FIGS. 3A and 3B show the motion of the several splines thatmake up the distal electrode array 36 as they move from the undeployedstate 43 to the deployed state 41. While in the undeployed state 43, thesplines lie together along side each other in a roughly tubular shapeseen in FIG. 3A. The splines typified by spline 50 deflect and blossommoving outwardly in a radial direction as the array is deployed to thedeployed state 41 as seen in FIG. 3B. This spline motion may be drivenby a pull wire (FIG. 15 element 52) in a pull wire embodiment.Alternatively the spline motion may be driven by a rotating screw 153that moves the screw driven pull member 159 seen within the array inFIG. 10 A and 10B. A rotatable member is used as a torque transmittingdevice from the handle to the screw member in the distal section. Therotatable member needs to be able to transfer torque while in a curvedenvironment. The rotatable member can be implemented in the form of atorque transmitting wire, coil, braid reinforced plastic tube or lasercut hypotube. The term rotatable member is intended to describe all ofthese alternative constructions. This alternative embodiment is calledthe rotary screw embodiment.

In the pull wire embodiment, the pull wire 52 is pulled back into thecatheter body of the deflectable segment 34 and the splines deform intoa shape reminiscent of a bulb of garlic. The pommel control 33 and theproximal spring 402 are connected to the pull wire 52 and motion of thepommel control 33 moves the splines to the deployed state.

The individual splines may carry several types of electrodes. The arrayof sensing electrodes typified by spline electrode 54 are used fornon-contact mapping and may also be used for assisting in the detectionand location of companion catheters in the heart chamber. Thesenon-contact electrodes are in the blood pool and they must receive anddetect very small voltages to perform the mapping operation. Locatorelectrode 55 is typical of such a spline electrode used for locationpurposes (also shown in FIG. 3A). Typically locator electrodes will lieon the greatest meridian of the deployed array 41 so that once deployedthey are quite far from each other as seen in FIG. 3B. However not everyspline need carry a locator electrode.

Each electrode on a spline is electrically connected to the cabling inthe handle. It is preferred that the signal from each individualelectrode be independently available to the hardware interface 20. Thismay be achieved by passing a conductor for each electrode through theconnection cable 17. As an alternative, the electrical connections maybe multiplexed in the catheter device 10 to minimize conductors.

It is important that the high-density electrode array be deployed into aknown, reproducible, and relatively stiff shape. The number ofelectrodes, their distribution and deployment shape, and stability inshape determine the limits of system performance. As electrode numberand deployment volume increase, the performance is improved. However itis both difficult and important to balance complexity, cost, andperformance with usability and patient benefit. An increase in electrodenumber and deployment size increases catheter 10 complexity andmaneuverability of the catheter 10 is compromised. Experimental worksuggests that a typical catheter 10 should have sixty-four sensingelectrodes and deploy to a three dimensional somewhat spherical shapewith a diameter of 18 mm. In order to know electrode locations foranalysis by the processing unit 24, the deployment shape must be tightlycontrolled. Therefore, several critical design features must be tightlycontrolled. The location of the electrodes 54 within the array must beaccurately placed. These electrodes 54 should also be placed in a mannerthat facilitates their use in close proximity to the endocardial surfacewhen the array is deployed. This requirement may necessitate anon-uniform distribution of the electrodes 54 as certain regions of thedeployed array are more likely to be positioned closely to theendocardium.

The deployed shape of the electrode array must be repeatable throughmultiple deployment cycles. For example, electrode locations need to beknown to within 1 mm between multiple deployments. The array should becapable of deploying to a known shape and subsequently dosing to a lowprofile (e.g. 8 French) for retraction. This shape change may be binaryor continuous, but in either situation, the shape must be repeatable andhave a known geometry at the time of data collection. The repeatableshape requirement is applicable to the electrode array shape in both thecircumferential and radial directions and represent a significant designchallenges. The inventive combination of fabrication technology,structural design and material choices cooperate together to achieve thedesign goal.

Also seen in FIG. 3B is a locator sensor 59. There are severalcommercially available 3-D location systems available for use in medicaldevices. In general location of the locator sensor 59 in space isreported by a base station located near the patient. This technology iswidely used in robotic surgery and need not be described in detail.Typically the locator sensor 59 would take the place of locatorelectrode 55.

FIG. 4A through FIG. 91) depict the formation of the array structurefrom a flexible printed circuit.

FIG. 4A shows a step in a preferred construction methodology for thedistal array segment 36. The distal array segment 36 is manufactured inpart from a flexible printed circuit 60 (“FPC”). This constructionmethodology has the advantage of repeatable high accuracy and lowmanufacturing cost. To construct the FPC 60, the material is initiallyfabricated in a planar form seen in FIG. 4A. In the planar condition, aseries of apertures 62 are cut through the FPC 60 at one end typified byhole 62. Together the series of apertures 62 form a bonding band 70. Atthe opposite more proximal end of the FPC 60 there is formed atermination band 106. The planar FPC 60 is also slit to free theindividual splines. Conventional laser processing is well suited to thisfabrication step.

FIG. 4B shows a process where the planar FPC 60 is wound around a majoraxis 61 bringing first edge 63 toward second edge 65.

FIG. 4C shows the two edges juxtaposed with both ends fixed. Togetherthe bonding band 70 and the termination band or section 106 complete acylindrical form. In general the distal bonding band 70 is fixed byencapsulation and the termination band is fixed by anchoring or bondingit to the deflection segment of the catheter.

FIG. 4D shows that with both ends fixed, the splines typified by spline50 may be moved radially with respect to the axis 61.

FIG. 5A shows that the ring of apertures 62 that together from a bondingband 70. In the figure, the edges of the gap are seen in close proximityat reference numeral 72.

FIG. 5B shows the use of the bonding band 70. Note that the edges may beheld together with a melted polymer or adhesive or other plastic orthermoplastic material that is applied to the interior and exterior ofthe tubular structure. This thermoplastic formed-in-place plug 74encapsulates the inside and outside of the FPC 60 providing an unusuallyrobust and durable structure that permits reliable deployment of thesplines.

FIG. 6A shows the FPC 60 in plan view. This view reveals the severalslits typified by slot or slit 108 which taken together form theindividual splines such as spline 50. These slits 108 extend from thedistal bonding section or band 70 to the termination section 106. Holes62 appear in the bonding band 70 and additional slits 110 are formedwithin the termination section 106 to facilitate attachment to thedeflectable section of the catheter.

The splines typified by spline 50 of the FPC 60 serve to position theelectrodes typified by electrode 54 along the length of the FPC 60. Thesplines 50 also carry interconnecting metal traces (not shown) thatserve to electrically connect the electrodes to pads in the terminationsection 106. The splines 50 are separated from each other using slits108. The slits are thin gaps that are cut in the FPC using one of manycutting techniques that may include laser cutting, die cutting orchemical etching. The slits 108 of the exemplary FPC are cut using alaser so as, to position slit location precisely.

The distribution of the electrodes 54 may be tightly controlled in thedesign of the FPC 60. For example, in FIG. 6A we note that electrodesare distributed more densely in the distal tip area. It should beappreciated that any desirable electrode distribution may beaccomplished using this method.

FIG. 6B shows the FPC 60 in cross-section. The various layers are not toscale. Some layers described are very thin while other thick, not alllayers are depicted in the figure for clarity. In particular, very thinlayers are not shown explicitly in the drawings. The FPC is constructedusing a relatively thick core insulating layer 86. The core layer 86 ofthe exemplary circuit is constructed of a 50 um layer of polyimide.Alternative materials and thickness core layers may be used to obtainthe desired mechanical and process characteristics. The core insulatinglayer 86 is coated with a top metallization layer 88 and a bottommetallization layer 90. Each of the exemplary metallization layers isdeposited by first sputtering a thin layer (˜0.1 um) of titanium overthe core insulating layer 86. The titanium layer serves as an interfacelayer to adhere additional metallization to the core insulating layer86. The metallization layers 88 and 90 can be added by furthersputtering and/or plating of additional metal over the titanium layers.The exemplary metallization layers 88 and 90 are sputtered with a goldlayer over the titanium layer and then further plated with gold untilthe total thickness of the metal layers measures 2 um. It should benoted that other conductors such as copper may also be used. It is alsonecessary to provide electrical connection between metal layers 88 and90 for the purpose of connecting circuit features that reside on eachlayer. A connection can be formed by constructing a via 96 between thetwo metallization layers. A via can be formed by creating a hole throughboth metallization layers 88 and 90 and the core insulating layer 86.Electrical connection is then made by plating the walls of the holebetween the two metallization layers forming a metal connection 96between the metallization layers 88 and 90. The FPC is furtherconstructed by providing a top covercoat 92 over the top metallizationlayer 90. The top covercoat 92 serves to insulate portions of the topmetal layer 88 from external contact. The top covercoat has openings 98placed in regions where it is desired to have the top metal layerexposed to external contact. For example a mapping electrode 54 may havethe covercoat above it exposed and be sputtered or plated onto the topmetal layer 88 as seen in FIG. 6B.

In the exemplary construction of FIG. 6B, the covercoat 92 of the FPC isformed by a 25 um layer of liquid photoimageable polyimide. Thephotoimageable polyimide covercoat is exposed and developed to preciselylocate geometric features on the exterior surface to create bloodcontacting electrodes, using similar registration and optical techniquesused to fabricate other features on the FPC.

A bottom covercoat 100 is applied to the bottom metal layer 90 in orderto insulate the bottom metal layer 90 from external contact. It may benecessary in some applications to enable the bottom covercoat 100 tohave openings similar to the openings 98 of the top covercoat 92. Suchapplications may require external contact to the bottom metal layer 90.One important application for the mapping electrodes 54 is to sense lowvoltage biological signals. The biological signals of interest aregenerally in the tens of microvolts to several millivolt range inamplitude and are time varying in the frequency range of 0.05 Hz toseveral kHz. The detailed design of the Flexible Printed Circuit (FPC)layers and electrodes in particular impact the noise level of themeasurement system. Reducing the impedance of the electrochemicalinterface between the electrode and blood reduces overall system noise.

Although a wide range of materials may be used to reduce impedance, ourpreferred electrode materials are selected from a small group which havedemonstrated to us that they are especially well suited for this design.We prefer to select electrode materials for blood contact from the groupof gold, stainless steel, platinum, platinum-iridium, titanium nitride,platinum black or iridium oxide (in order of highest to lowestimpedance). Electrode materials are applied using an electroplating orsputtering process.

At present our preferred FPC 60 and electrode construction includes anFPC with a polyimide core layer with gold metal layers. The bloodcontacting electrodes are gold coated with iridium oxide.

In addition to material properties, electrode area has a profound impacton impedance and in the design the electrode area may be increased to awidth limited by the dimension of the spline and further limited by thepresence of other metal features including traces.

It is also be possible to increase the surface area of electrodesthrough surface finishing. Roughening of the electrode surface can beaccomplished through anyone of several mechanical or chemical surfacetreatments.

FIG. 6B also shows that a stiffener layer 102 may be applied over thebottom cover coat 100 as seen in FIG. 6B. The stiffener layer 102 mayhave various thickness and material compositions in order to achieve thedesired rigidity of the FPC in order to control the deployed shape. Theexemplary FPC of the invention is comprised of a 50 um thick polyimidestiffener 102 over the bottom covercoat 100. It should be appreciatedthat other materials such as PEEK or Nitinol may be used as a stiffener.The stiffener 102 is adhered to the to the bottom covercoat using apolyimide adhesive layer. Other adhesives, and in particular, pressuresensitive adhesives may also be used for this purpose. Additionalstiffener layers may be applied over stiffener layer 102. Stiffenerlayer 120 serves to increase the stiffness of the circuit in selectedareas.

The termination section 106 also serves to provide a region where theFPC may be bonded to the outer catheter shaft during installation.

FIG. 7 shows a metallization layer in plan view. The dark areas in FIG.7 are the metallization traces created by the processes described inconnection with FIG. 6A, but the core layer and other layers are notshown for clarity. Subpanels seen in the figure are enlargements of themetallization trace pattern to show various features. For example, thetermination section 106 of the FPC of FIG. 6A is shown as traces 108 inthis figure. The traces are metallic layers that serve to create aregion where the FPC can be connected to wire or cabling that serve toelectrically connect the FPC to circuitry or connectors in the proximalsection of the catheter. The wire or cabling may be attached to the FPCat a series of termination lines as designated by reference numeral 112.

It should be appreciated that a number of metallization layers rangingfrom 1 to 16 may be used. The addition of layers is helpful in carryingadditional signals given a width constraint such as the spline width.

FIG. 8A shows how to increase the stiffness of the exemplary FPC of FIG.6 forming areas of high stiffness 124 and areas lower stiffness 126.

FIG. 8B shows how to control the deployed shape of the array bycontrolling the stiffness of the exemplary FPC forming areas of highstiffness 124 and areas of lower stiffness 126.

FIG. 8C shows a representative shape where stiff zones 124 or areasinterspersed with less stiff areas 126 can create a complex array shapeupon deployment. In the figure, there is more stress in the thin areas126 which bend more readily than in the stiffer regions 124.

FIG. 8D shows thicker regions with additional stiffener layers formingstiff zones 124 while less stiff material yields a less thick moreflexible area 126. The use of alternating stiffness areas helps tocontrol the distribution of stress as well as determine deployed shape.In this embodiment the spline shape is segmented into relatively rigid“straight” sections 124 followed by “hinged” areas 126. The detaildrawing of FIG. 8E shows the high stiffness area 124 next to a lowerstiffness area 126.

FIG. 9A shows how to increase the stiffness of the exemplary FPC of FIG.6 forming areas of high stiffness 124 and areas of lower stiffness 126that are spaced along the spline.

FIG. 9B shows that a stiffener layer 102 may be applied over the bottomcovercoat 100 as described in connection with FIG. 8B.

FIG. 9C shows a representative shape where stiff zones 124 or areascombined with less stiff areas 126 can create a complex array shape upondeployment. In the figure there is more stress in the thin areas thatbend more readily than in the stiffer regions 124. Together the addedmaterial allows for a smoothly varying distribution of stress along thespline.

FIG. 9D shows thicker regions with additional stiffener layers formingstiff zones 124 while less stiffener material yields a less thick moreflexible area 126. The use of alternating stiffness areas helps tocontrol the distribution of stress as well as determine deployed shapeyielding a continuously curved spline having a smoothly varyingdistribution of stress along the spline. The detail drawing in FIG. 9Eshows a stiff area 124 next to a less stiff area 126.

Thus it is shown that distal deployable electrode array segment isformed from a multiple layer flexible printed circuit slit to formsplines and rolled about said longitudinal central axis to form saiddistal electrode array The slits may be wider or narrower along thelength of the spline and this non-uniform shape characteristic resultsin control of the shape of the electrode array in the deployed position.It should also be appreciated that the stiffer elements along thesplines also create a non-uniform shape characteristic that results incontrol of the final shape of the electrode array in the deployedposition or state.

To provide the physician with visual feedback of the array state(deployed or undeployed), the array needs to be visible on fluoroscopy.This may be accomplished in several ways. The circuit may be made fromand enhanced with an additional layer made from materials that are, inthemselves, radiopaque such as gold, platinum, and/or tungsten,including others. Alternatively, a radiopaque substrate can be added tothe array to enhance visualization upon deployment. This substrate canbe in the form of marker bands, coiled wire, or radiopaque ink. Inparticular, the radiopaque ink may contain suspended tungsten that hasradiopaque properties. This type of ink could be applied through aprinting process on the undeployed electrode assembly while in the FPCconfiguration.

FIG. 11, FIG. 12, and FIG. 13 show differing strategies to reduce bloodclotting on the array. It is conventional practice to administeranticoagulants to a patient undergoing these procedures. However is veryuseful to eliminate blood clotting on the catheter itself FIG. 11, FIG.12, and FIG. 13 show several techniques that may be adopted to achievethis goal. Continuous or episodic injection of saline or heprinizedsaline are contemplated with the embodiments of FIG. 11 and FIG. 12. Itshould be noted that various coating such as hydrophilic coatings,hepirnized coatings, and parylene may also be applied to cathetersurface alone or in combination with the techniques presented in thefigures in order to reduce clot.

FIG. 11 shows a distal segment having a fluid supply lumen associatedwith the pull wire feature 52. Fluid 57 introduced into a hub at theproximal end of the catheter emerges from aperture 53 and aperture 55 toflood the array and prevent blood clots from adhering to the splines.

FIG. 12 shows a porous membrane associated with the pull wire featurelocation in the distal array segment to allow fluid introduced into thecatheter under pressure to emerge from the porous sheath 200 and floodthe array to prevent blood clots from adhering to the splines.

FIG. 13 shows a collapsible corrugated section 202 preventing blood fromentering the catheter opening in the distal array structures.

FIG. 14 shows a strategy for constraining the deployment providing tightcontrol over the final shape of the deployed array. For example tether300 may emerge from the central shaft in FIG. 14 to restrain the motionof the splines or limbs.

As described previously, it is or great importance for the catheter tosupport controlled articulation while keeping the deployed shape known.FIG. 15 and FIG. 10 describe two different embodiments that meet thisrequirement. The mechanism in FIG. 15 relies on a spring to accomplishindependence of the two mechanisms, while the mechanism of FIG. 10relies on threads in distal array segment 36 to accomplish the samegoals.

FIG. 15 is a simplified schematic diagram of the catheter that serves todescribe the interaction between the articulation and deflection aspectsof the catheter. The figure serves to explain the operation of oneembodiment of the array deployment construction. In brief, the array ispulled open with a pull wire. The array is biased by a spring 400 toreturn to the undeployed state. The pull wire 52 extends from the handle30 where it is anchored to a proximal spring 402 to the distal tip 37where it is anchored in the distal tip. The proximal spring 402 is inturn connected to the pommel or deployment control 33. As the deploymentcontrol 33 is retracted the pull wire pulls the distal tip 37 toward thehandle 30. The tip motion is guided by tube 406 sliding over a bushing408. This motion can continue until the tube bottoms out on surface 404.This mechanical stop determines the amount of shortening of the distalsegment. As a consequence this stop also serves to limit the deployedstate of the deployable array. In this figure the splines are not shownfor clarity (for comparison see FIG. 16B). This motion also compressesthe distal spring 400. If tension of the pull wire is eased then thedistal spring 400 restores the array to the undeployed state.

The pull wire 5 and the proximal compensator spring 402 have a nominallength that gets longer or increases as the deployment control movesinto the locked position. The increase in length comes from the tensionsupplied to the spring that increases spring length. This process isseen dearly comparing FIG. 16A to FIG. 16B.

FIG. 16C corresponds to deflection or articulation of the catheterdeflectable segment 34. The deflection control causes the catheter todeflect in the plane of the figure and this displaces the pull wire 52within the elongate catheter body 32. As the pull wire moves from aconcentric to an offset position within the body 34 the relative lengthof the pull wire compared to the length of the shaft changes. This isseen most clearly at reference numeral 410.

The proximal spring 402 compensates for and takes up this motion bycontracting slightly while still providing enough tension in the pullwire to keep the distal array fully deployed.

FIG. 17 shows the interplay of tension in the pull wire and displacementof catheter components. As the control 33 is activated and moved towardthe deployed condition, tension rises in the wire as seen at panel A.When the array is full deployed the mechanical stop engages the proximalspring and force preferably remains constant as the control reaches thedeployed state depicted in panel B. In this state, the catheter is inthe state depicted in FIG. 16B. During deflection, as seen in FIG. 16C,the relative motion of the pull wire and its housing causes the springtension to falloff in the proximal spring as seen in panel C to D, whilethe distal array remains against its stop. In this fashion, the distalspring and its mechanical stop cooperate with the proximal spring forceto stabilize the array deployment during catheter deflection. FIG. 10Aand FIG. 10B show an alternative embodiment for deploying the array ofthe catheter. In this embodiment a screw 153 is positioned in the distalsegment of the catheter. This screw 153 is rotated by a rotatable memberor shaft 161 driven by a knob located in the handle which is notillustrated in the figures. The rotatable member 161 is keyed to thedistal array segment 36 with the construction in section 155. Theconstruction provides the counter-force against which distal arraysegment 26 is deployed and retracted. This construction also isolatesthe screw 153 and prevents it from being influenced by tension in therotatable member 161. A complimentary nut forms a pull member 159 isfree to slide over the stationary screw. The pull member 159 has an endanchored in the distal tip of the array and the traction supplied by thescrew 153 causes the pull member 159 to move retrograde deploying thesplines 50 of the array as seen in FIG. 10B. This construction rendersthe deployment function independent of the articulation function of thecatheter since the deployment function is unaffected by the tension onrotatable member 161. In addition, this embodiment permits the array todeploy to known continuous intermediate states or positions between thefully retracted and fully deployed states. These continuous intermediatepositions are useful in mapping operations where it is desirable tointroduce the catheter into structures smaller than its fully deployeddiameter while maintaining accurate knowledge of electrode locations.Electrode locations are determined from the amount of deployment whichcan be derived from the number of rotations employed by the rotatablemember during deployment.

1-18. (canceled)
 19. A catheter comprising: an elongate catheter bodyhaving a distal end and a proximal end; a proximal handle segment havingan articulation control and a deployment control, said proximal handleconnected to said proximal end; an intermediate segment connected tosaid handle segment; a deflectable segment connected to saidintermediate segment, said deflectable segment adapted to articulate ina plane through an angle in response to said articulation control; adistal array segment connected to said deflectable segment, said distalarray segment including a deployable electrode array that can move froma first retracted position to a second deployed position; saiddeployable electrode array formed from a flexible printed circuit slitto form splines and rolled about the major axis, the splines of theflexible printed circuit including first regions having a firststiffness and second regions that include one or more stiffener layersand have a second stiffness that is greater than the first stiffness,the stiffness of the first and second regions at least partiallydetermining the shape of the electrode array in the deployed position,said distal array segment has a non-uniform distribution of electrodesin the array with the electrodes being distributed more densely inregions of the deployed array that are more likely to be positionedclosely to the endocardium.
 20. The catheter of claim 19 wherein: eachspline in said deployable electrode array has a non-uniform shapecharacteristic resulting in control of the shape of the electrode arrayin the deployed position.
 21. The catheter of claim 19 wherein: saiddistal array segment has a uniform and symmetrical distribution ofelectrodes in the array.
 22. The catheter of claim 19 wherein; saiddeployable electrode array having bonding apertures at an end of thearray adapted for encapsulation to form and retain said tubular shape.23. The catheter of claim 19 wherein; said deployable electrode arrayhaving bonding apertures at an end of the array adapted forencapsulation by a thermoplastic material to form and retain saidtubular shape.
 24. The catheter of claim 19 wherein: said deployableelectrode array is formed from a flexible printed circuit comprising: aninsulating layer; a first metal layer supported by a first surface ofthe insulating layer and a second metal layer supported by a secondsurface of the insulating layer, the first and second metal layerscomprising an electrode material selected from the group consisting of:gold, stainless steel, platinum, platinum-iridium, titanium nitride,platinum black and iridium-oxide; an overcoat layer supported by thesecond metal layer configured to insulate the second metal layer; afirst stiffener layer supported by the overcoat layer; and a secondstiffener layer that is separate from the first stiffener layer anddisposed on portions of the first stiffener layer to form the secondregions that have the second stiffness that is greater than the firststiffness.
 25. The catheter of claim 19 further comprising: a fluiddelivery lumen to flood the distal array segment with a fluid injectedinto the catheter.
 26. The catheter of claim 19 further comprising: aradio-opaque pattern applied to the distal array segment such that thepattern changes during deployment to provide a discernable radiographicimage to confirm deployment.
 27. A catheter comprising: an elongatecatheter body having a distal end and a proximal end; a proximal handlesegment having deployment control, said proximal handle segmentconnected to said proximal end; a distal array segment including anelectrode array having a non-uniform distribution of electrodes with theelectrodes being distributed more densely in regions of the deployedarray that are more likely to be positioned close to the endocardium,said distal array segment connected to said distal end; said electrodearray formed from a flexible printed circuit and comprising: aninsulating layer comprising a first side and a second side; a firstmetallization layer coated with iridium oxide on the first side of theinsulating layer, the first metallization layer configured to increasethe surface area of the first metallization layer; a secondmetallization layer on the second side of the insulating layer; and anelectrical connection between the first metallization layer and thesecond metallization layer; and a radio-opaque pattern applied to thedistal array segment such that the pattern changes during deployment toprovide a discernable radiographic image to confirm deployment.
 28. Thecatheter of claim 27, wherein first metallization layer comprises aplurality of metal layers.
 29. The catheter of claim 27, wherein firstmetallization layer comprises: a titanium layer supported by theinsulating layer; a gold layer supported by the titanium layer; and aniridium-oxide layer supported by the gold layer.
 30. The catheter ofclaim 27, wherein the first metallization layer comprises: an interfacelayer supported by the insulating layer; a conductive layer comprising acopper or gold layer supported by the insulating layer; and aniridium-oxide layer supported by the conductive layer.
 31. The catheterof claim 27, wherein the first metallization layer comprises: aconductive layer comprising a copper or gold layer; and an iridium-oxidelayer supported by the conductive layer.
 32. The catheter of claim 27,wherein second metallization layer comprises a plurality of metallayers.
 33. The catheter of claim 27, wherein the electrical connectionbetween the first metallization layer and the second metallization layercomprises a metallization layer in a via that extends through the firstmetallization layer, the insulating layer, and the second metallizationlayer.
 34. The catheter of claim 27, wherein the radio-opaque comprisesone or more of marker bands, coiled wire, and radiopaque ink.
 35. Acatheter comprising: an elongate catheter body having a distal end and aproximal end; a proximal handle segment having an articulation controland a deployment control, said proximal handle connected to saidproximal end; an intermediate segment connected to said handle segment;a deflectable segment connected to said intermediate segment, saiddeflectable segment adapted to articulate in a plane through an angle inresponse to said articulation control; a distal array segment connectedto said deflectable segment, said distal array segment including adeployable electrode array that can move from a first retracted positionto a second deployed position, wherein said deployable electrode arrayis formed from a flexible printed circuit comprising: an insulatinglayer; a first metal layer supported by a first surface of theinsulating layer and a second metal layer supported by a second surfaceof the insulating layer, the first and second metal layers comprising anelectrode material selected from the group consisting of: gold,stainless steel, platinum, platinum-iridium, titanium nitride, platinumblack and iridium-oxide; an overcoat layer supported by the second metallayer configured to insulate the second metal layer; a first stiffenerlayer supported by the overcoat layer; and a second stiffener layer thatis separate from the first stiffener layer and disposed on portions ofthe first stiffener layer to form the second regions that have thesecond stiffness that is greater than the first stiffness.
 36. Thecatheter of claim 35 further comprising: a fluid delivery lumen to floodthe distal array segment with a fluid injected into the catheter. 37.The catheter of claim 35 further comprising: a radio-opaque patternapplied to the distal array segment such that the pattern changes duringdeployment to provide a discernable radiographic image to confirmdeployment.
 38. The catheter of claim 35 wherein: said distal arraysegment has a non-uniform distribution of electrodes in the array withthe electrodes being distributed more densely in regions of the deployedarray that are more likely to be positioned closely to the endocardium.